1. Field of the Invention
The present invention relates to a determination apparatus for determining a type of a recording medium and an image forming apparatus equipped with the determination apparatus.
2. Description of the Related Art
In a conventional image forming apparatus, a user sets a type of a recording medium (hereinafter also referred to as “paper type”), for example, by setting at a computer serving as an external apparatus or using an operation panel provided in the main body of the image forming apparatus. By setting a type of a recording medium, image forming conditions can be changed according to a type of a recording medium, and image formation is carried out under the conditions suitable for the type of the recording medium. To reduce the load of such user setting through a computer or an operation panel, recently, an image forming apparatus has been provided with, for example, a sensor capable of determining a type of a recording medium inside the image forming apparatus so that a type of a recording medium is automatically determined.
For example, “Japanese Patent Application Laid-Open No. 57-132055” discusses a method in which, when a grammage of a recording medium is measured with use of an ultrasonic wave, a propagation time of an ultrasonic wave between an ultrasonic transmitter and an ultrasonic receiver is calculated in advance, and the grammage is measured based on the calculated propagation time.
However, the environment where a recording medium determination apparatus is disposed is not always under a constant temperature and atmospheric pressure. Therefore, a variation in the environment brings about a change in the propagation speed of an ultrasonic wave in the air, so that detection based on a propagation time calculated in advance may not produce an accurate measurement result.